“A Low Blow” - Copperwood Press

By John T. Frye W9EGV
“A Low Blow”
from the March, 1961
Popular Electronics
Copperwood Press • Colorado Springs, Colorado
This story has been excerpted from Carl & Jerry, Their Complete Adventures,
Volume 4. The print book contains 24 stories, originally published in Popular
Electronics from January 1961 through December 1962. Printed books may
be ordered through Lulu.com at the following URL:
http://www.lulu.com/copperwood
An index with summaries of all Carl & Jerry stories may be found here:
http://www.copperwood.com/carlandjerry.htm
© 1961, Popular Electronics Magazine
Reprinted by Permission.
Additional Material © 2007 Copperwood Associates, Inc.
All Rights Reserved
This file may be freely redistributed as long as it is not modified.
Copperwood
Associates
Colorado Springs, Colorado
Carl and Jerry
March 1961
A Low Blow
I
t was two whole weeks since Carl and Jerry had talked face to
face. Jerry had been home from school sick with influenza, and
the boys’ parents had kept them apart to prevent Carl’s catching the
virus infection. The two had managed to keep in touch by chatting
on the phone, by talking over their ham stations, and—since their
bedroom windows faced each other—even by blinking Morse code
on flashlights from one window to the other. But Jerry had finally
recovered sufficiently to be down in his basement laboratory this
warm, windy Saturday morning, and to have Carl visit him.
“Hi, Jer,” Carl said gruffly as he came in through the outside
basement door. “How’s my puny pal? You look kinda pale around
the gills.”
Jerry turned away from the large, wide-mouthed glass jar sitting
on the workbench in front of him to bestow a fierce scowl on his
friend.
“Don’t ‘puny pal’ me, you big ox! Disgustingly healthy people
make me sick!”
“Now, now, there!” Carl murmured with mocking solicitude.
“We mustn’t get upset. Remember: we are not well. And what are
we doing with that goldfish bowl?”
“I am getting ready to test my infra-sonic microphone,” Jerry said
curtly, turning back to the fishbowl that had a thin membrane of
rubber stretched over the top. Inside was a small, brass-topped glass
jar containing some transistors and other components mounted
on a little circuit board. Two tiny twisted wires of the sort used in
3
4
From: The Complete Carl and Jerry Volume 4
record-player
tone
arms came out of a
wax-sealed hole in the
bottom of the jar, ran
up over the edge of
the bowl beneath the
rubber
membrane,
and were connected
to the input of a tape
recorder sitting on the
workbench.
“I
need
more
information than that,” Carl cheerfully confessed. “What is this
‘infrasonic’ jazz? I’ve never heard you mention a project like that
before!”
“In physics you should have learned that sound recognized as such
by the human ear goes down in frequency to about 12-15 cycles,”
Jerry explained, “but there are other compression and rarefaction
waves in the atmosphere at much lower frequencies. These are
called ‘infra-sonic waves,’ and we are surrounded by them even
when our ears hear nothing.
“They obey the same laws as sound waves: Their speed varies as
the product of the square root of the absolute temperature and a
constant related to the conducting medium.
“At 32°F,” he continued, warming to the subject, “sound travels
about 1087 feet per second in air, and the speed increases as the
temperature rises. The rate at which sound power is absorbed
and dissipated into heat depends on the frequency. The fraction of
sound power absorbed per unit distance of propagation is roughly
proportional to the square of the frequency. That explains why
you hear the bass drum of an approaching band first, and it also
means that only low inaudible frequencies can be propagated great
distances.”
Carl started to say something, but Jerry didn’t give him a chance.
“When the volcano Krakatoa exploded in 1883 in the East Indies,
inaudible waves from this disturbance traveled around the world
several times with a pressure so great that it produced readable
A Low Blow
5
deflections on barographs. The impact of the great meteor that fell in
Siberia in 1908 had the same result. During World War I, it was noticed
that cannon fire could be heard within a radius of 100 kilometers, and
often beyond 200 km., but not between 100 and 200 km.”
“The sound waves must have been skipping the way our radio
waves do,” Carl noted.
“Exactly! Observers figured that something far above the earth
must be deflecting the sound waves back down. The only thing that
could do so would be a layer of air warmer than the air at the earth’s
surface, which would speed up the top edge of the sound wave
entering it at an angle and bend the wave back toward the earth.
By listening for the lowest audible frequencies and by checking the
transit time of the wave from the source to the distant observer,
those smart cookies figured out where and how warm that layer of air
had to be! Very recent information gathered by our space probes
confirmed their calculations.
“As you go up in a quiet atmosphere,” Jerry went on, “the
temperature falls sharply at first and then zigzags back and forth
until you reach an altitude of about 105 km. From that point on
up, for at least a considerable distance, the temperature increases
steadily, reaching much higher values than here—”
“Just a cotton-picking minute,” Carl interrupted. “You didn’t
know all this when you got sick. How did you get so smart?”
“Some time back,” Jerry explained, “I noticed a newspaper article
about how the National Bureau of Standards was carrying on
experiments on the detection and recording of infrasonic waves. I
wrote the Bureau asking for more information, and Mr. Paul Walsh
and Mr. Donald M. Caldwell kindly sent me a lot of interesting
information about their installation near Washington, D. C.”
“How do they work it?”
“They have four infrasonic microphones set up at different
locations several miles apart. Signals from each mike are fed to a
central location where they are amplified, bandpass-filtered, and
recorded as ink-on-paper traces. By noticing the difference in time
of the signal’s arrival at various mike locations, its speed and sourcedirection can be determined.”
6
From: The Complete Carl and Jerry Volume 4
“I can’t imagine what sort of mike you’d use to pick up signals
of one or two cycles per minute,” Carl muttered with a thoughtful
frown.
“Neither could I,” Jerry agreed, “but the dope I got says the mike
is a condenser type with a diaphragm of thin, specially-formed
brass mounted on a reference volume. One side of the diaphragm
connects to a noise-reducing pickup pipe. Movements of the
diaphragm modulate the frequency of an oscillator.”
“I see—I think,” Carl said doubtfully, “but what’s this about a
noise-reducing pipe?”
“When the mike diaphragm is exposed directly to the open air,
pressures produced by the wind develop a lot of signal-masking
noise. These specially designed metal pipes lie on top of the
ground and are each about 1000 feet long. Each pipe has 100 small
holes distributed along its length. A signal traveling toward the
microphone along the length of the pipe is attenuated very little,
but random variations in pressure caused by wind turbulence are
greatly reduced.”
“What sort of sounds, or whatever you call ‘em, are picked up?”
“Well, on May 5, 1960, when the weather bureau reported 19
tornadoes and funnel clouds in Oklahoma, Texas, and Kansas
in a four-and-a-quarter-hour period, the microphones recorded
waves of periods between 12 and 50 seconds with speeds about
equal to that of sound in air and with pressures slightly less than
one dyne per square centimenter. Hearing a tornado 1000 miles
away is sharp listening! A system of detectors like this could
track tornadoes. In fact, another installation is planned near
Boulder, Colorado.
“On August 18,1959,” Jerry continued, “sound pressure
produced by the big earthquake in Montana was observed at the
NBS Washington laboratories. An earthquake wave traveling along
the earth’s crust moves the surface up and down like the cone
of a giant speaker and sends sound waves almost vertically into
the atmosphere. Information gleaned from these waves valuably
supplements data gathered by seismographs regarding the nature of
a quake and its original source.
A Low Blow
7
“Magnetic storms
also produce strange
‘sound’ waves of
periods greater than
20 seconds with a
trace velocity up
to three times the
speed of sound.
These waves usually
arrive from the
north during magnetic storms, and they have a large angle to the
surface of the earth. The Bureau hopes to study them to learn more
about the interaction of the sun and the earth’s magnetic field.”
“H
OW did you make your mike, and what are you going to do
with it?” Carl asked, as the ground shook with a low growl of
distant thunder.
“I stretched a diaphragm of very thin brass shim stock tight over
a little steel hoop. Another disc of brass mesh wire is separated
from the shim stock disc by a thin insulating washer. This assembly,
mesh disc down, is mounted on top of the little glass jar with an
airtight seal. The homemade printed-circuit board inside the jar
contains two transistorized crystal oscillators and a diode mixer
to combine their outputs. The capacitor formed by the diaphragm
and the screen is across one of the crystals. The two oscillators are
tuned—you can tune a crystal oscillator a little, you know—so that
their frequencies are only one kilocycle apart; and this means that
the difference frequency of 1000 cycles comes out of the mixer. Any
movement of the brass diaphragm produced by pressure waves
against it is translated into a frequency shift of the crystal oscillator
associated with the condenser mike, and an accompanying change
in the beat-frequency tone coming out of the mixer.”
“Hey, old buddy, that’s pretty sharp!” Carl applauded.
“Nothing any bored American boy shot full of antibiotics
couldn’t do!” Jerry replied modestly. “The roughest job was drilling
two holes through the bottom of the glass jar without breaking it.
Leads from the mixer come out one, and the other is covered with
a brass disc with a very tiny hole punched in it with a needle. That
8
From: The Complete Carl and Jerry Volume 4
keeps our mike from responding to very slow pressure changes
caused by barometric variations, yet allows it to respond to waves
with periods up to several minutes in length.”
He switched on the tape recorder, and soon a 1000-cycle note was
heard from the speaker. At the same time, a meter connected across
the recorder speaker rose to half-scale.
“That’s a simple audio frequency meter I’ve calibrated to indicate
frequencies between 100 and 5000 cycles,” Jerry answered Carl’s
questioning look. “We don’t have any ink-on-paper recorders, but
that meter pointer will swing back and forth in step with any lowfrequency waves received. Tape-recording the changes in tone will
give us a chance to double-check on any waves we think we observe.
Now, let’s see what happens when we test it out.
“I drop this little steel ball on the rubber membrane, like so, and
this causes a very small increase in the pressure inside the bowl. See
that meter kick down? If I’ve calculated right, it will start creeping
back in a couple of minutes as air leaks through the tiny hole to
equalize the pressures on both sides of the diaphragm.”
The microphone passed the test with flying colors. It responded
to very small changes in pressure; yet, if the pressure was left applied,
the tone returned to 1000 cycles in the space of a few minutes.
“Now all you need is that pipe pickup,” Carl remarked.
“We’ve got it!” Jerry said promptly. “Didn’t you notice that the
men laying that new 8” gas line in the street stopped directly in front
of the house last night? Welders will weld the joints together Monday
and put the pipe down in the trench, but right now it stretches out
to the west on top of the ground for a couple of thousand feet with
the joints all neatly butted tight together. I’m hoping small air leaks
at these joints will serve as the holes in the pipe used by the National
Bureau of Standards.
“The beauty of it all is that the weather bureau has a tornado alert
out for the area to the west of us. We may be lucky enough to hear
a tornado! Suppose you go out, Carl, and fasten our mike in the end
of the pipe with this wooden collar, and run this twisted pair from it
into the cellar window.”
A Low Blow
C
9
ARL carried out
the
assignment
quickly because huge
drops of rain had begun
spattering down. When
the wires were connected
to the input of the tape
recorder, the meter pointer
immediately began to hunt
restlessly up and down the
scale.
“What we’re looking for
is a slow, rhythmic swing
of the meter pointer,”
Jerry shouted above the roar of the wind outside, which had begun
whipping up the trees and was now pounding furiously at Jerry’s
house.
But there was nothing slow or rhythmic about the pointer as
it swung wildly up and down. Suddenly it began to go up and up,
hesitated for a moment, and then fell back to zero and stayed there.
The tone disappeared.
“Something’s happened to our mike,” Jerry shouted as he
grabbed up his jacket and headed for the door. At the top of the steps
he stopped dead in his tracks and stared up into the northwestern
sky. Carl, looking over his shoulder, saw the writhing, twisting,
unmistakable shape of a small tornado funnel high above the
ground and moving off to the north. Even as the boys watched, the
little tornado disintegrated.
They raced over to the pipe and pulled out their mike. The thin
brass diaphragm was ruptured, with the jagged corners curled
outward somewhat like the petals of a flower.
“Jer, look way down there at the other end of the pipe,” Carl said
in awe. Jerry followed his pal’s pointing finger and saw that the
straight line of the pipe was broken four or five blocks away, and
the sections of pipe were scattered over the street like jackstraws. A
small temporary tool house nearby had been smashed to kindling
and the tools strewn about like scraps of paper.
10
From: The Complete Carl and Jerry Volume 4
“That little twister must have dabbed down squarely on top of the
pipe and then hopped back up,” Carl said thoughtfully.
“Yeah, and it sucked on that end of the pipe hard enough to bust
our mike diaphragm at this end,” Jerry finished. “The tornado dealt
us a low blow. We aren’t really sure our infrasonic mike works.”
“I’m not complaining,” Carl said philosophically as he started
back for the house. “We’re mighty lucky the twister was sucking on
that end of the pipe and not on our end!”
Carl & Jerry Books from Copperwood Press
Carl & Jerry: Their Complete
Adventures, Volume 1
Stories from October 1954
through December 1956,
with all original illustrations.
208 pp. $15.95
Carl & Jerry: Their Complete
Adventures, Volume 2
Stories from January1957
through December 1958,
with all original illustrations.
190 pp. $15.95
Carl & Jerry: Their Complete
Adventures, Volume 3
Stories from January1959
through December 1960,
with all original illustrations.
190 pp. $15.95
Carl & Jerry: Their Complete
Adventures, Volume 4
Stories from January1961
through December 1962,
with all original illustrations.
196 pp. $15.95
Carl & Jerry: Their Complete
Adventures, Volume 5
Stories from January1963
through November 1964,
with all original illustrations.
208 pp. $15.95
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